MTATE LAN BOARD
E-533 O, NMarch 1941
( BUREAU OF
SECOTTON ROOT APHIDS AND THEIR CONTROL
By C. F. Rainwater,
Division of Cotton Insect Investigations
Cotton root aphids are small sucking insects commonly called root
lice or blue bugs. They are similar in appearance to the familiar leaf
aphids or plant lice that are so often seen on the leaves of cotton and many
other plants. All aphids feed by inserting their slender beaks in the plant
tissues and sucking the plant juices, but the cotton root aphids differ from
the leaf aphids in that so far as known they feed entirely on the underground
parts of the plants. Their soft roundish bodies are about 1/16 inch in
length when fully grown. Some of the adults are winged but most of them are
wingless. The adults give birth to living young, and reproduction continues
throughout the winter in the South, although at a slow rate during cold
weather. Root aphids are helpless insects, and, while capable of crawling,
they cannot move for any distance through the soil to the roots on which
they feed. Consequently a relationship has developed between the root aphids
and field ants whereby the ants tunnel through the soil and carry the aphids
from plant to plant and place them on the roots. The aphids secrete a
sweetish liquid, or honeydew, that is the principal source of the ants'
food and thus repay them for their help. The relation between the ants and
the root aphids is thus of mutual advantage. The aphids have become depend-
ent upon the ants for locating their food and are seldom found without the
attending ants. This dependence on the ants is used as a basis for aphid
control, since disturbance or destruction of the ants reduces the number of
Kinds of Cotton Root Aphids and Their Distribution
It was formerly thought that the corn root aphid (Anuraphis maidi-
radicis (Forbes)) was the only species of root aphid attacking cotton,
but recent studies have shown that two other species not previously known as
cotton pests in the United States are responsible for part of the damage.
Since all three species are called cotton root aphids, common names based
on the predominant colors have been used locally as follows:
(1) The white cotton root aphid for Trifidaphis phaseoli (Pass.).
(2) The green cotton root aphid for Anuraphis maidi-radicis (Forbes).*
(3) The brown cotton root aphid for Rhopalosiphum subterraneum Mason.
The white cotton root aphid causes the most serious damage to cotton,
and infested plants usually die. The color ranges from amber through yel-
lowish white to milky white. The very young aphids or nymphs are amber
colored, changing to whitish as they reach maturity. The adults are more
robust than the adults of the other two species and also less active. This
species '.''as not known to attack cotton prior to 1934, but since that time it
has beeii found injuring cotton in southeastern Virginia, eastern and central
North Carolina, and South Carolina. Judging from the increasing number of
complaints received in recent years, this species is apparently spreading or
becoming more important as a cotton pest. Every examination of severely
injured cotton with a large number of plants killed by root aphids has shown
this species to be present, though usually one or both of the other species
were also present.
The green cotton root aphid has long been called the corn root aphid
because it is an important pest of corn. This species has been known as a
cotton pest for many years and is the one from which the common name "blue
bugs" has arisen. However, its color is more green than blue, ranging from
bluish giiten to dark green. The green cotton root aphid is the most widely
distributed of the three species and occurs on corn throughout the United
States east of the Rocky Mountains. It has been found attacking cotton,
however, only in southeastern Virginia, eastern and central North Carolina,
South Carolina, and eastern and central Georgia.
The brown cotton root aphid ranges in color from a very light, almost
reddish brown in the nymphs to a very dark or purplish brown in the adults.
This species likewise was not known to attack cotton until recently, but
since 1934 it has been found on cotton in eastern North Carolina and in
northeastern and north-central South Carolina.
The cotton root iphids feed on the underground portions of a wide
variety of plants. Since tI.ey continue feeding throughout the winter, a
succession of food plants throughout the sear is necessary. When other food
plants are abundant the aphlid damage to cotton is increased, and control of
the aphids is more difficult.
The green cotton root aphid feeds on the roots of corn, several common
legumes, cockleburs, smartweed, a numl-er of grasses, or in brief on prac-
tically every weed ordinarily found in corn or cotton fields in the South.
This variety of food plants is probably more responsible than any other
factor for this species being more widely distributed than the other two.
The white cotton root aphid is ui:nble to survive on the roots of as
many different plants au, tIe j'.reen. The principal plants other than cotton
are the l','umies. Peas, .oyLvaiis, crotalaria, lespedeza, vetch, and clover
are its most common food plants. Some of these are available as food
throughout the year. This aphid also attacks a number of vegetables.
The brown cotton root aphid is also a rather general feeder but has
not been found on the roots of as many plants as the green cotton root aphid.
It has been found on the roots of okra, butterbeans, soyl-eans, cocklebur,
rabbit tobacco (or life everlasting), evening primrose, and goose grass.
Other host plants of all three species will probably be found as studies
Since the cotton root aphids are entirely subterranean in habit they
are seldom seen unless a special search is made. They feed on the roots of
cotton from the time the seeds sprout until the first squares appear on the
plants. They cause the greatest damage early in the season before the
seedlings become well established. Their sucking of sap causes the young
plants to become yellowish, unhealthy, stunted, and in many cases to die.
The damage resembles that caused by cool weather or seedling diseases, with
which it is often confused. In many instances the plants are severely stunted
in growth but recover, causing great irregularities in the size of the plants.
All three species of aphids cause similar injury, although the severity of
the damage varies considerably with the different species. The injury caused
by the green and brown root aphids is usually more in the nature of stunting
or retarding the growth of the plants, although plants are killed where the
infestation is heavy. The white root aphids nearly always kill the infested
cotton plants. Frequently two or all three species are present on the same
plants. Often the stand is greatly reduced and the remaining plants are
stunted over a considerable acreage (fig. 1). All the plants in a row may be
killed for considerable distances as the ants move the aphids from plant to
plant along the row through underground tunnels. Infested fields are usually
"spotted" or "ragged" in stand and appearance. Often only a portion of a
field is severely damaged, but at times whole fields are ruined and have to
be abandoned. The stunted plants that recover are later in fruiting and
therefore more subject to boll weevil attack than normal plants.
How to Recognize Root Aphid Injury to Cotton
The presence of unhealthy plants early in the season, with ant hills
occurring around their bases, is an almost positive indication that aphids
are on the roots (fig. 2). Many farmers erroneously think that the ants are
damaging the cotton. But if a plant is removed with the soil around the
roots intact, and the soil is then carefully removed from the roots,
large numbers of these aphids will frequently be seen clustered around the
stem and roots. Often the roots will be so completely covered with aphids
that it would be difficult to place the point of a pin on the root without
touching an aphid. If the plants are simply pulled from the soil, however,
no aphids will likely be found, as this pulling has a tendency to strip them
from the roots. If the ground is soft, one may push his hand into the soil
and remove the plant with the soil around its roots intact. But if the ground
is hard, the best method of removing the plant with the aphids atta:Vhed is to
use a trowel or a small garden spade.
Many different kinds of ants are ordinarily found in a cotton field,
but only one kind has been found of enough importance to be considered in
the control of cotton root aphids. This ant is Lasius niger variety neo-
niger Emery and is closely related to the species commonly called the corn-
field ant. It is light brown and relatively small, and the mounds which it
makes by excavating soil for its burrows are usually found around the base
of some plant. This is in contrast to the majority of ants' mounds seen in
a field, which are usually in open spaces some distance from plants. Also,
the mounds made by this ant in cotton fields in the spring of the year
seldom contain any subsoil, as they excavate only deep enough to attend
the aphids, and at this season the roots do not reach into the subsoil.
Therefore ant mounds which contain soil different in texture from the top-
soil are not likely to indicate the presence of root aphids.
Experiments conducted at Florence, S. C., on the control of cotton
root aphids since 1935 have included the use of repellents, soil fumigants,
seed treatment, and ant poisons. The best results were obtained from the use
of an ant poison or bait prepared as follows;
One-half pound of tartar emetic
One pound of sugar
One quart of cane syrup
One gallon of water
These materials should be thoroughly mixed and brought to a slow
boil while being stirred occasionally. The liquid bait is then mixed with
cottonseed hulls. About 6 pounds of cottonseed hulls will absorb this
amount of poisoned bait and is sufficient to treat from A acre to 1 acre of
cotton. The bait is distributed in the field by placing small handfuls in
the center of each third row approximately 10 feet apart in the row. The
ants quickly come to this bait and feed ravenously. The majority of the
ants in the poisoned area usually disappear within 24 hours, and at the end
of 48 hours practically none can be found.
It has been found that the test time to apply the bait is just as the
cotton is Leginning to sprout. Usually a rain occurs between the time of
planting and the time the cotton begins to come up. This packs the soil
and makes it easier for the ants to come to the bait. Best results have been
obtained by applying the bait shortly after a lain on a warm, sunny day,
as the ants are usually more active then. It may sometimes te necessary to
make two or three applications of the bait at intervals of a week to 10 days
to get the desired control, but experiments to date indicate that practical
and economical control can be obtained by its use. The tartar emetic bait,
if applied as described above and before a large number of the plants have
been killed, will greatly reduce the amount of injury the root aphids will
cause. TLis bait is relatively inexpensive. The cost of the materials
necessary to prepare bait for treating 1 acie of cotton, including the cost
of cot'oiineed hulls, is about 35 cents. It is also easily and rapidly ap-
plied, and, though poisonous if taken internally, it may safely Le handled
with ordinary precautions,
Cultural Practices as Aids in Control of Cotton Root Aphids
It has been observed for several years that root aphids cause more
injury to cotton following certain crops than others. Where cotton follows
cotton, tobacco, or any of the small grains (oats, wheat, or rye) the injury
from root aphids is usually not so severe as where cotton follows corn, soy-
beans, or cowpeas. This is probably due to the smaller number of weed host
plants that grow among the former crops and the fact that corn, soybeans,
and cowpeas are favorite hosts of the aphids.
Early in the spring the root aphids feed on the roots of many weeds
that come up in the cotton fields. Here they multiply rapidly, and large
numbers are moved by the ants to cotton roots as soon as the cotton germi-
nates. Frequent cultivation early in the spring kills the weed_ on which
they live and breaks up the ants' burrows. Frequent cultivation during the
early stages in the growth of the cotton, particularly following a rain,
keeps the soil loose and pulverized and makes it more difficult for the ants
to construct tunnels for moving the aphids from one cotton plant to the next.
It has also been noted that when cotton is planted early and retarded
in growth by cool weather the aphids have a chance to become established on
the roots before the cotton begins to grow. If root aphids are present, a
few days' delay in planting cotton frequently results in stronger, more
Seed that has been treated with ethyl mercury chloride (Ceresan) dust
is being used by large numbers of farmers. This treatment has resulted in
better stands of cotton and in plants freer from seedling diseases and more
able to withstand root aphid attack.
The following cultural practices will aid in controlling cotton root
(1) Break the land thoroughly and keep it free of weeds for several
weeks prior to planting.
(2) Have the seedbed loosely pulverized at the time of planting.
(3) If possible, avoid planting cotton on land following corn, soy-
beans, or cowpeas.
(4) Treat seed with an organic mercury (Ceresan) dust.
(5) Do not plant too early.
(6) Cultivate frequently in the early stages of growth, and as soon
as possible after each rain.
(7) Make side applications of nitrates at chopping time to stimulate
The information now available indicates that the use of poisoned bait
for the ants and the suggested cultural aids will control root aphids on
cotton. Further experiments are under way to determine the relation of
different host plants to the abundance of root aphids on cotton. It is hoped
that crop rotations will be developed that will fit into approved farm
practices and'will further reduce root aphid damage.
Figure 1.-A field of cotton with a perfect stand at the
beginning of the season that has been severely injured by
cotton root aphids. Note that some of the plants are very
much stunted in growth and many of them have been killed.
Near Florence, S. C., June 18, 1939.
Figure 2.-A portion of a cotton row showing the presence of
root aphids on the roots of seedling cotton, as indicated
by the stunted growth and by the ant hills around the bases
of the plants. The plants in the center are being severely
attacked by root aphids, and many if not all of them will
die.* The ants construct tunnels in the ground and move the
aphids from plant to plant. Near Florence, S. C., Nay 12, 1939.
UNIVERSITY OF FLORIDA
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